Not long after his appointment as director of Rogue One: A Star Wars Story, Gareth Edwards made something of a faux pas.

He was sitting down with the props masters, discussing which weapons they would use for the Imperial Deathtroopers and Stormtroopers.

"They had all these different designs. I picked them up and I remember saying that one of them felt so antiquated. It felt like something that they had in World War II. Then they told me that was exactly the Stormtrooper weapon from A New Hope," says Edwards, who made his name with the 2010 science-fiction film Monsters and the 2014 version of Godzilla.

In the original Star Wars trilogy, which kicked off in 1977 with Episode IV: A New Hope, the Imperial troops wielded modified Sterling submachine guns previously used by the British Army.

Edwards, 41, continues: "When George Lucas was making those films, they didn't have much money, so they were grabbing real- world guns and just making a few modifications.

"Looking at them now, I think it was that realism and that worn, used world-feel, which made them feel fresh."

With his faux pas firmly behind him, he is keen to ensure that his film matches the early Star Wars films in terms of tone and design.

Rogue One is one of the standalone Star Wars stories that will accompany the continuation of the main series, whose next instalment, Episode VIII, is scheduled to be in cinemas in December next year. The next standalone film, planned for a 2019 release, will focus on a young Han Solo.

Rogue One takes place just before the events that play out in Episode IV, in which the rebels destroy the Death Star, having stolen the secret plans to its design.

Producer Simon Emanuel says: "We are making a period movie, a 1970s-feeling movie. Gareth wanted to make sure that we have a look that feels exactly like A New Hope, so you could sit and watch both films, one after the other, and they would feel the same."

The latest movie centres on a heroine called Jyn, played by English actress Felicity Jones, an orphan who is raised by the Rebellion, a group that opposes the growing menace that is the Empire.

"Jyn is our heroine," says Emanuel, 41. "She is a rebel who partners Cassian, who has a chequered past. He works for Rebel Intelligence and he partners Jyn to go on a mission to find Jyn's father and then, ultimately, the plans for the Death Star."

Jyn and Cassian's journey takes them to a planet that is known as Jeddah. The set for this portion of the movie was built on the backlot at Pinewood Studios in England and it looks a lot like the desert planet of Tatooine, which plays such a prominent role in Episode IV and also Episode VI: Return Of The Jedi (1983).

Rogue One eventually takes the heroine and her friends to the moment that opens A New Hope, whose opening scene fans will remember: Darth Vader and his Star Destroyer chasing down a rebel ship with Princess Leia on board.

Edwards says working towards that exact moment proved very liberating for him as a film-maker. "With this film, we knew where we were heading and it all came down to how we begin that journey," he says, "and so it was the polar opposite of what you normally have. I think it was easier.

"The big challenge was where do we begin and which characters do we pick and how do we do it in a way that feels like Star Wars. You can do a million different ideas, but just sticking Star Wars on a poster doesn't make it a Star Wars film.

"It was about trying to get that magical combination that we all grew up with, that mixture of epic canvas, but with an emotional core, something about a small group of people that are connected by family and things like that. It felt very Shakespearean and that was what George Lucas was borrowing from when he did the originals."

Although he speaks glowingly of his film, it has been reported that Disney, the studio that owns the franchise after paying Lucas US$4 billion for the rights in 2012, stepped in to insist on reshoots.

The Hollywood Reporter claimed that the screenwriter Tony Gilroy was paid US$5 million to rework the movie's ending.

Many observers had apparently wondered if the film was too dark or violent. After all, on getting the job, Edwards had said he wanted to put the "war" into Star Wars.

But he refutes the claims that the original Rogue One was too bleak.

"Definitely, I am very pleased with the tone of the film," he insists. "We didn't compromise the tone of the movie at all."

A war movie, he says, is about much more than the combat. "I know that it sounds silly to say that, but it is also the aftermath and the price that you pay and so Jeddah in our movie is meant to represent an occupied territory and the consequence of not doing anything and not being able to do anything against the Empire.

"You're left thinking, 'If we don't stop this kind of thing and put an end to it, we will witness this kind of oppression across the whole galaxy.' So throughout, the film is peppered with imagery of the consequences of not acting and letting an evil take over. I didn't want to make just a war film."

He says that the secret to much of the original films' success was Lucas' ability to blend different genres.

"What George did so well was to ensure Star Wars was not one genre. People like to summarise them as science-fiction films or fantasy films, but really, you could say Star Wars is a biblical epic set in space, or a Western. There's a bit of samurai films in there too.

"Star Wars is all different genres put into a melting pot and stirred. We definitely poured a lot of war into our melting pot, but there are also other things."

For a sequence in Rogue One that features a battle on a beach, Edwards had hoped it could resemble the opening to Saving Private Ryan (1998) in terms of its tense and grim action. He also wanted to recall the opening to Episode V: The Empire Strikes Back (1980) with its land battle on ice planet Hoth.

"Hoth was one of the highlights of the original trilogy and you think, 'Let's do something with trench warfare, but without snow,' and you start to look back on that and then you realise - I can't remember the exact number - but the ice battle is something like eight shots. It is so efficient.

"As a kid, I spent years playing with Star Wars figures and the AT-AT Walkers and so in my mind, that battle went on for hours," he adds. "But like I said, it's very efficient. We do have some ground warfare, which I am happy to say is not as efficient but it definitely ticks that box in my mind, in terms of seeing the visuals that I was very keen on as a kid."

When Jyn begins her adventures, she recruits a number of allies, alongside Cassian (Diego Luna), who bring plenty of warrior skills. One is K-2SO, an Imperial battle droid which has been captured and reprogrammed by Cassian to spy for the Rebellion.

The other two characters are humans, Chirrut, a blind monk with amazing martial art skills, and Baze, a former assassin and sniper who is trying to change his ways. These characters are brought to life by Ip Man star Donnie Yen and Chinese actor-director Jiang Wen, respectively.

The China-born, US-raised Yen, 53, recalls: "I was thrilled to be invited onto Star Wars, but already I had plans for another movie. I needed a solid reason to be a part of it and I didn't want to be away from my kids for too long.

"We went back and forth a lot and it was my kids who persuaded me to sign up. They wanted to see Stormtroopers. They said, 'You've got to do this movie!' They came to the set and had some fun. And now they can say, 'My father beats up Stormtroopers!'"

Jiang, 53, needed even more persuading, and again, the Star Wars producers owe much to kids.

"The first time I talked to Gareth Edwards, I said that I wasn't really interested," he says through a translator.

"But my son read the script and he left me a note: 'Dad, we need to talk.' When we spoke, he said I had to join up. He said that Baze is a great hero and also a fun hero. He has a lot of humour. That was good because I was worried that the character might not be important in the film."

He adds with a laugh: "My son and also my daughter said that my movies back home were not very interesting for kids, so I should definitely do this one. And I'm so glad that I did."

• Rogue One: A Star Wars Story opens in Singapore tomorrow.